Differential Antioxidant Response to Supplemental UV-B Irradiation and Sunlight in Three Basil Varieties.

Three basil plant varieties (Ocimum basilicum var. Genovese, Ocimum × citriodorum, and Ocimum basilicum var. purpurascens) were grown under moderate light (about 300 µmol photons m-2 s-1) in a glasshouse or growth chamber and then either transferred to an open field (average daily dose: 29.2 kJ m-2 d-1) or additionally exposed to UV-B irradiation in a growth chamber (29.16 kJ m-2 d-1), to reveal the variety-specific and light-specific acclimation responses. Total antioxidant capacity (TAC), phenolic profile, ascorbate content, and class III peroxidase (POD) activity were used to determine the antioxidant status of leaves under all four light regimes. Exposure to high solar irradiation at the open field resulted in an increase in TAC, total hydroxycinnamic acids (HCAs, especially caffeic acid), flavonoids, and epidermal UV-absorbing substances in all three varieties, as well as a two-fold increase in the leaf dry/fresh weight ratio. The supplemental UV-B irradiation induced preferential accumulation of HCAs (rosmarinic acid) over flavonoids, increased TAC and POD activity, but decreased the ascorbate content in the leaves, and inhibited the accumulation of epidermal flavonoids in all basil varieties. Furthermore, characteristic leaf curling and UV-B-induced inhibition of plant growth were observed in all basil varieties, while a pro-oxidant effect of UV-B was indicated with H2O2 accumulation in the leaves and spotty leaf browning. The extent of these morphological changes, and oxidative damage depended on the basil cultivar, implies a genotype-specific tolerance mechanism to high doses of UV-B irradiation.

Combined Spraying of Boron and Zinc During Fruit Set and Premature Stage Improves Yield and Fruit Quality of European Hazelnut cv. Tonda di Giffoni.

Boron (B) and zinc (Zn) are essential micronutrients of plant nutrition programs in orchards for securing the crop quality and yield. Although orchard supplementation with B and Zn is a common practice to overcome deficiencies or maintain their optimal levels, the efficiency of combined B and Zn spraying in relation to European hazelnut (Corylus avellana L.) phenological stage has not been investigated so far. Leaf and kernel mineral and functional traits were studied in cultivar Tonda di Giffoni after B and Zn spraying in four phenological stages. During the 2016/2017 season, 9-year-old trees were sprayed with B (0, 800, and 1,600 mg L-1) and Zn (0, 400, and 800 mg L-1) under three treatments: B0+Zn0, B800+Zn400, and B1600+Zn800 implemented in three spring application programs scheduled from October to December (P1: four times, P2: early two times, and P3: late two times). B and Zn treatments in P1 and P3 led to higher Zn concentration both in leaves and in kernels compared with non-sprayed trees. Stabilized nut production increased 2.5-fold under B800+Zn400 in all three programs. Kernel/nut ratio improved in both B+Zn treatments in P1 and P3, while the percentage of blank nuts was reduced compared with B0+Zn0. Increased radical scavenging activity in B+Zn-treated kernels and leaves was not attributed to the accumulation of phenolics in P3 compared with B0+Zn0, whereas B and Zn spraying reduced the level of lipid peroxidation in both studied organs. According to the results, combined B and Zn should be sprayed at the end of spring (P3) on hazelnut plantations in temperate areas such as Southern Chile, whereas early applications (P2) showed an irregularity in nut production and functional traits in nuts. Moderate and partialized rates of B and Zn and the time of implementation contribute to improving the quantitative and qualitative features crucial for future sustainable hazelnut production.

Direct inhibition of photosynthesis by Cd dominates over inhibition caused by micronutrient deficiency in the Cd/Zn hyperaccumulator Arabidopsis halleri.

This work reveals, by imaging in vivo measurements in the Cd/Zn hyperaccumulator Arabidopsis halleri, in how far Cd stress affects macronutrient (Ca, K) and micronutrient (Fe, Zn) distribution in the leaves. We directly correlate these changes with biophysics of the photosynthetic light reactions. Plants were grown for 2 months at 10 µM Zn (=control), and supplemented with 10, 15, 50 or 75 µM Cd. Direct imaging of OJIP transients revealed that bundle sheath cells were more sensitive to Cd toxicity than mesophyll cells further from the vein. Progressive inhibition of photosystem (PS) II reaction centres and decrease in quantum yield of electron transport between QA and QB and further to PSI acceptors was observed. This was correlated with the decreased dynamics of QA re-oxidation and lower operating efficiency of PSII. Analysis by a benchtop micro X-ray fluorescence device showed that Cd mostly accumulated in the veins, and restricted Fe and Zn distribution from the veins, especially in the 75 µM Cd, while K concentration increased in the whole leaf. Calcium distribution was apparently not affected by Cd, but Cd excess inhibited trichome formation and thereby diminished total Ca concentration in the leaves. The results point to differential tissue sensitivity to Cd, evident by heterogeneous inhibition of photosynthesis. Part of this may be a result of selective disturbances in the leaf nutrient homeostasis. The better photosynthetic performance away from the veins compared to the bundle sheath cells, however, indicates that direct inhibition of photosynthesis by Cd dominates over inhibition caused by micronutrient deficiency.

Quercetin 7-O-glucoside suppresses nitrite-induced formation of dinitrosocatechins and their quinones in catechin/nitrite systems under stomach simulating conditions.

Foods of plant origin contain flavonoids. In the adzuki bean, (+)-catechin, quercetin 3-O-rutinoside (rutin), and quercetin 7-O-ß-D-glucopyranoside (Q7G) are the major flavonoids. During mastication of foods prepared from the adzuki bean, the flavonoids are mixed with saliva and swallowed into the stomach. Here we investigated the interactions between Q7G and (+)-catechin at pH 2, which may proceed in the stomach after the ingestion of foods prepared from the adzuki bean. Q7G reacted with nitrous acid producing nitric oxide (˙NO) and a glucoside of 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone. (+)-Catechin reacted with nitrous acid producing ˙NO and 6,8-dinitrosocatechin. The production of the dinitrosocatechin was partly suppressed by Q7G, and the suppression resulted in the enhancement of Q7G oxidation. 6,8-Dinitrosocatechin reacted further with nitrous acid generating the o-quinone, and the quinone formation was effectively suppressed by Q7G. In the flavonoids investigated, the suppressive effect decreased in the order Q7G≈quercetin>kaempferol>quercetin 4'-O-glucoside>rutin. Essentially the same results were obtained when (-)-epicatechin was used instead of (+)-catechin. The results indicate that nitrous acid-induced formation of 6,8-dinitrosocatechins and the o-quinones can be suppressed by flavonols in the stomach, and that both a hydroxyl group at C3 and ortho-hydroxyl groups in the B-ring are required for efficient suppression.